Fibre reinforced polymer composite pipes

ABSTRACT

A fiber reinforced polymer composite pipe includes first and second ends and defines a central axis running in a longitudinal direction from the first end to the second end, and the pipe including at least one non-linear portion along the central axis between the first end and the second end. A first material extends continuously from the first end to the second end, the first material being a fiber reinforced polymer material comprising fiber reinforcement in a polymer matrix and having an electrical resistivity determined by an electrically conductive fiber reinforcement and/or an electrically conductive additive in the polymer matrix; and a second material arranged at the at least one non-linear portion and extending discontinuously between the first end and the second end, and has an elastic modulus greater than the elastic modulus of the first material in the longitudinal direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 16/721,211filed Dec. 19, 2019 which claims priority to European Patent ApplicationNo. 19275091.7 filed Oct. 7, 2019, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to composite (e.g. fiber-reinforcedpolymer) pipes and in particular to pipes having at least one non-linearportion or more complex geometries.

BACKGROUND

Composite materials, such as fiber-reinforced polymers, are used in awide variety of applications where parts with high strength but low massare required. For example, carbon or glass fiber-reinforced polymer(FRP) composite materials are often used to produce structuralcomponents (e.g. struts, connectors), force-transmitting components(e.g. drive shafts, push rods) and fluid transfer conduits (e.g. fuelpipes) in the aerospace and automotive industries. Components suitablefor these applications must have high strength to handle the largeforces involved, but also need to minimise weight for fuel saving and/orperformance reasons.

Modern composite winged aircraft do not provide adequate protection tothe fuel system from lightning strikes. The fuel pipes in the fuelsystem must have a low enough electrical conductivity to preventelectrical discharge from a lightning strike but sufficient electricalconductivity to prevent static electrical build-up. It is known totailor the electrical conductivity of composite fuel pipes by mixing adispersion of electrically conductive particulate filler into a glassreinforced polymer material, for example as disclosed in WO 2009/087372.

In addition to electrical conductivity properties, it remains achallenge to form composite pipes that also have sufficient stiffness towithstand pressurised flow for a range of pipe geometries. It would bedesirable that fuel pipes, for example, are not constrained to a linearshape. However, complex geometries introduce extra demands as there maybe a tendency for a pressurised pipe to deform at any bends. Deflectionsin a composite pipe can cause the pipe to come loose from its endconnectors.

There remains a need for improvements in composite pipes.

SUMMARY

According to the present disclosure, there is provided a fiberreinforced polymer composite pipe. The pipe includes: a first end and asecond end, the pipe defining a central axis running in a longitudinaldirection from the first end to the second end, and the pipe includingat least one non-linear portion along the central axis between the firstend and the second end. A first material extends continuously from thefirst end to the second end, the first material being a fiber reinforcedpolymer material comprising fiber reinforcement in a polymer matrix andhaving an electrical resistivity determined by an electricallyconductive fiber reinforcement and/or an electrically conductiveadditive in the polymer matrix. A second material arranged at the atleast one non-linear portion and extending discontinuously between thefirst end and the second end, the second material being a carbon fiberreinforced polymer material comprising carbon fiber reinforcement in apolymer matrix and having an elastic modulus provided by the carbonfiber reinforcement. The elastic modulus of the second material isgreater than the elastic modulus of the first material in thelongitudinal direction.

Composite pipes in accordance with this disclosure do not run straightalong the central axis as they include at least one non-linear portion(such as a bend) between the first end and the second end. In otherwords, such pipes run in a non-constant axial direction. In someexamples, the second end may be offset from the first end as a result ofthe at least one non-linear portion. In some examples, the first end andthe second end may be co-linear but with one or more non-linear portionsbetween them, e.g. forming a pipe that has a complex shape rather thanbeing straight.

It will be appreciated that composite pipes in accordance with thisdisclosure have the first material extending continuously from end toend, which means that the overall electrical conduction path alwaysincludes the first material. The second material provides a greateraxial stiffness as a result of its carbon fiber reinforcement, whichmight otherwise provide an electrical conductivity higher than desired.However, as the second material does not extend continuously from end toend, the overall electrical conductivity of the pipe can be tailored bythe first material. For example, the electrical resistivity of the firstmaterial may be designed to compensate for excessive conductivityresulting from the carbon fiber reinforcement in the second material.Meanwhile, the second material beneficially provides increased axialstiffness for the non-linear portion(s) that are most susceptible todeformation. As both the first and second materials are electricallyconductive, there are no discontinuities in the electrical conductionpath along the pipe. The pipe's end-to-end conductivity requirements, aswell as wall thickness requirements, can be met by suitable tailoring ofthe first material.

In some examples, the first material has an electrical resistivity atleast partially determined by an electrically conductive fiberreinforcement. For example, the electrically conductive fiberreinforcement may comprise chopped carbon fiber. In such examples, thepolymer matrix may be a thermoplastic, e.g. polyether ether ketone 13“PEEK”.

In at least some examples, the first material is a fiber reinforcedpolymer material comprising chopped carbon fiber reinforcement in thepolymer matrix, and having an electrical resistivity at least partiallydetermined by the chopped carbon fiber reinforcement. In such examples,the chopped carbon fiber reinforcement may be present in the firstmaterial in an amount of between 5% and 15% of the material by weight orvolume.

Where a lower conductivity fiber may be required, e.g. to compensate forthe second material, the fiber reinforcement may comprise glass fibers,polymeric (e.g. aramid) fibers, and/or alumina silica. Such electricallynon-conductive fiber reinforcement may be mixed with chopped carbonfibers in some examples. In addition, or alternatively, thenon-conductive fiber reinforcement may comprise one or more continuousfibers.

In at least some examples, in addition or alternatively, the firstmaterial is a fiber reinforced polymer material comprising anelectrically non-conductive fiber reinforcement in the polymer matrix,and having an electrical resistivity at least partially determined by anelectrically conductive additive in the polymer matrix.

The electrically conductive additive can be incorporated into the firstmaterial in varying amounts to achieve the desired electricalresistivity for a particular application. As mentioned above, a suitableelectrically non-conductive fiber reinforcement may include one or moreof: glass fibers, polymeric (e.g. aramid) fibers, or alumina silicafibers. In such examples, the polymer matrix may be a thermoset, e.g.epoxy resin.

In at least some examples, the electrically conductive additive ischosen from one or more of: carbon black, graphene, carbon nanotubes,and conductive metal oxide particles. For example, conductive metaloxide particles may be made of antimony tin oxide (ATO) or indium tinoxide (ITO).

In examples in which the conductive additive comprises carbon black, thecarbon black may be present in the first material in an amount ofbetween 1% and 5% of the material by weight or volume.

In examples in which the conductive additive comprises carbon nanotubes,the carbon nanotubes may be present in the first material in an amountof between about 0.1% and 0.8% of the material by weight or volume, forexample about by weight or volume.

In at least some examples, the electrically conductive additive ispresent in the polymer matrix in an amount up to 40%, 30%, 20%, 10%, 5%,2%, 1% or 0.5% of the polymer matrix by weight or volume.

The composition of the first material may be tailored to provide adesired level of electrical conductivity, for example as generallydescribed in WO 2009/087372, the contents of which are herebyincorporated by reference. The electrical conductivity or resistivity ofthe first material may be chosen to ensure that the composite pipe has adesired level of resistance per unit length, e.g. taking into accountthe thickness of the pipe. The overall resistance per unit length of thecomposite pipe may be specified for a particular application orenvironment.

In at least some examples, the first material has an electricalresistivity selected such that the composite pipe has an overallresistance per unit length of between 50 kΩ per meter and 4 MΩ permeter, and preferably between 150 kΩ per meter and 1.4 MΩ per meter.

In at least some examples, the first material has an electricalresistivity selected such that the composite pipe has an overallresistance per unit length of less than 1.25 MΩ per meter.

The main purpose of the first material is to meet the pipe's end-to-endelectrical conductivity requirements. The first material may be closerto an inner surface or an outer surface of the pipe. The first materialmay be sandwiched between layers of the second material at thoselocations where the second material is present.

In at least some examples, the first material takes the form of an innerpipe or an outer pipe.

The overall end-to-end electrical conductivity of the pipe may beaffected by the wall thickness of the pipe. A minimum wall thickness maybe stipulated, e.g. for pressurised applications such as fuel pipes. Thethickness of either the first material and/or the second material may beadjusted as appropriate to meet wall thickness requirements. In at leastsome examples, the composite pipe has wall thickness in the range of1-10 mm.

In at least some examples, the first material is formed by automatedfiber placement (AFP). In such examples, the polymer matrix may be athermoplastic material.

In at least some examples, the first material is formed by filamentwinding of the fiber reinforcement, for example by winding continuousfibers at low angles relative to the central axis of the pipe. In suchexamples, the polymer matrix may be a thermoplastic material.

While various conventional manufacturing techniques for fiber-reinforcedpolymer composites may be employed to make composite pipes according tothe present disclosure, it has been recognised that some techniques maybe better suited than others for making non-straight pipes and morecomplex pipe geometries.

In at least some examples, the first material is formed by resintransfer molding (RTM) using a braided preform for the fiberreinforcement. In such examples, the polymer matrix may be a thermosetmaterial.

When penetrating through a mesh of fibers, the fibers may act to filterout the carbon black or other conductive additive in the polymer matrixmaterial. This is not desirable as the conductive characteristics of thefirst material may be caused to vary over the length of the pipedepending on the percentage of additive filtered out. Using RTM methods,described further below, the filtration effect of the fibers isminimised as the resin is distributed over the longitudinal extent ofthe mold before radially penetrating the fibers. This effect can beoptimised by injecting the resin into the mold under pressure and/or byapplying a vacuum to the mold.

As is described below, in at least some examples it may be efficient toform both the first material and the second material in a single RTMprocess. A braided preform may be used for the fiber reinforcement ofthe first and/or second material. Such constructions can result in thecomposite pipe having an improved impact performance, for example ascompared to a composite material made by filament winding.

As the second material does not extend continuously between the firstand second ends of the pipe, its carbon fiber reinforcement can betailored to provide a desired elastic modulus without concerns aboutexcessive electrical conductivity.

In at least some examples, the second material is a carbon fiberreinforced polymer material comprising continuous carbon fiberreinforcement in a polymer matrix. Continuous fiber reinforcement canmake the second material stiffer than discontinuous or chopped fibers.

The polymer matrix of the second material may be a thermoplastic or athermoset. This may depend on the technique(s) used to apply the secondmaterial, as is discussed further below.

In some examples, the second material could possibly be formed byfilament winding of the carbon fiber reinforcement, for example bywinding continuous carbon fibers at low angles relative to the centralaxis of the pipe. However, filament winding is usually limited to aminimum angle of about 30 degrees relative to the central axis of thepipe.

In other examples, techniques are used to achieve angles of 30 degree orless relative to the central axis of the pipe. In particular, arrangingat least some of the carbon fiber reinforcement at 0 degrees, i.e. axialfibers, greatly improves the axial stiffness and strength.

It may be preferable that at least some of the continuous carbon fiberreinforcement extends at an angle of between −30 degrees and +30 degreesrelative to the central axis of the pipe. In at least some examples,substantially all of the continuous carbon fiber reinforcement extendsat an angle of between −30 degrees and +30 degrees relative to thecentral axis of the pipe.

It may be preferable that at least some of the continuous carbon fiberreinforcement extends at an angle of between −5 degrees and +5 degreesrelative to the central axis of the pipe. In at least some examples,substantially all of the continuous carbon fiber reinforcement extendsat an angle of between −5 degrees and +5 degrees relative to the centralaxis of the pipe.

It may be preferable that at least some of the continuous carbon fiberreinforcement extends at an angle of about 0 degrees relative to thecentral axis of the pipe.

For example, the second material may be formed by placing pre-wovencarbon fibers including at least some axial fibers at 0 degrees.

In at least some examples, the second material is a carbon fiberreinforced polymer material formed by automated fiber placement (AFP).In such examples, the polymer matrix may be a thermoplastic.

A preferred technique is to braid the continuous carbon fiberreinforcement so as to achieve one or more desired fiber angles and useresin transfer molding to set the fiber preform in a thermoset matrix(such as epoxy resin). Thus, in at least some examples, the secondmaterial is a carbon fiber reinforced polymer material formed by resintransfer molding (RTM).

The carbon fiber preform may take the form of a triaxial braid. Atriaxially braided tube may comprise three sets of fibers braided orplaited together to make a pre-form sock as is known in the art ofcomposite materials.

In at least some examples, the continuous carbon fiber reinforcement isformed by a triaxially braided tube comprising a first group ofcontinuous carbon fibers extending substantially along the central axisof the pipe, a second group of continuous carbon fibers extending at anangle of +50-85 degrees (e.g. about +75 degrees) relative to the centralaxis of the pipe, and a third group of continuous carbon fibersextending at an angle of −50-85 degrees (e.g. about −75 degrees)relative to the central axis of the pipe. The second and third group ofcontinuous carbon fibers can contribute to both axial strength and hoopstrength.

In such examples, the first, second and third groups of fibers may beinterwoven to form the triaxially braided tube. In any example of thedisclosure, the first group of fibers could extend at an angle ofbetween −10 and 10 degrees, or more preferably between −5 and 5 degreesrelative to the central axis of the pipe. In any example of thedisclosure, the second group of fibers could extend at an angle ofbetween 60 and 90 degrees relative to the central axis of the pipe. Inany example of the disclosure, the third group of fibers could extend atan angle of between −60 and −90 degrees (300 and 270 degrees) relativeto the central axis of the pipe. Using current braiding machines, it isnot normally efficient to braid the second and third groups of fibers atan angle of more than +/−85 degrees or more than +/−75 degrees relativeto the central axis of the pipe.

It will be appreciated that the relative quantities and angles of thefirst, second and third groups of fibers in the triaxially braided tubecan be varied to meet the design requirements of a particular tube.

In some examples, the triaxially braided tube may be pre-formed and thenslid over the radially outer surface of a pipe made from the firstmaterial. Alternatively, the triaxially braided tube may be formed bybraiding directly around the radially outer surface of a pipe made fromthe first material.

In some examples, the triaxially braided tube may be pre-formed and thenslid over a former to set the second material at desired positions alonga pipe before the first material is formed over the top.

In other examples, the continuous carbon fiber reinforcement may beformed by a biaxially woven fabric or mesh comprising a first group ofcarbon fibers extending at about 0 degrees (i.e. substantially parallelto the central axis of the pipe) and interwoven with a second groups ofcarbon fibers extending at about 90 degrees (i.e. substantiallyperpendicular to the central axis of the pipe).

In any example of the disclosure, if necessary to increase the strengthof the second material against radial loads as well, additional carbonfibers may be circumferentially wound over the triaxially braided tubeor the biaxially woven fabric. This may be most beneficial when usedwith a triaxially braided material in which there are no fibersextending perpendicular or at about 90 degrees to the central axis ofthe pipe.

After the required arrangement of carbon fibers (for example, comprisingthe triaxially braided tube described above) has been placed intoposition, the polymer matrix e.g. resin is then added to form the secondmaterial. In any example of the disclosure, a RTM technique may be used.A two-part mold is placed around the pre-form and underlying pipe orformer. The mold is then clamped shut and a vacuum is applied while aresin such as epoxy resin is injected under pressure into the mold. Thecombination of injection under pressure and the applied vacuum draws theresin through the mold to penetrate radially into the carbon fibers.

In any example of the disclosure, quick or snap cure resins may be usedto reduce the time required for curing the resin in the second material.

Heat is then applied to the mold to cure the resin. This causes thefiber arrangement and the resin to set into a solid reinforced material.The mold may then be unclamped and opened so that the pipe including thesecond material at the non-linear portion(s) can be removed.

In some examples, the second material may be formed at the same time asthe first material, for example in a shared RTM or resin infusionprocess. In such examples, the fiber reinforcement of the first materialmay be formed by a first braided or woven preform, e.g. placed onto asuitable former or mandrel, and the carbon fiber reinforcement of thesecond material may be formed by a second braided or woven preformplaced next to the first braided or woven preform. For example, thesecond braided or woven preform may be placed on top of or inside thefirst braided or woven preform. After arranging the first and secondpreforms in a suitable mold, a polymer matrix material e.g. epoxy resinis then added to form the first and second materials. The polymer matrixmay be the same material throughout the composite pipe in such examples.Such manufacturing methods are further disclosed below.

In some examples, in addition or alternatively, the second material maybe selectively added to the first material in a subsequent process stepso as to be located at the non-linear portion(s) of the pipe.

In at least some examples, in addition or alternatively, the secondmaterial takes the form of a material layer selectively added at the atleast one non-linear portion.

The arrangement of a first material extending end-to-end and adiscontinuous second material, as disclosed herein, is ideal for formingcomplex pipe geometries including multiple bends. In at least someexamples, the pipe includes a plurality of non-linear portions along thecentral axis between the first end and the second end, and the secondmaterial is arranged at each non-linear portion.

In at least some examples, the composite pipe is a fuel pipe.

There is further disclosed herein a method of making a fiber reinforcedpolymer composite pipe comprising: providing a mold cavity shaped toform a pipe having a first end, a second end, and at least onenon-linear portion between the first end and the second end; placing oneor more fiber preforms in the mold cavity to form the fiberreinforcement of a first material extending continuously from the firstend to the second end; placing one or more carbon fiber preforms in themold at the at least one non-linear portion to form the fiberreinforcement of a second material extending discontinuously between thefirst end and the second end; and filling the mold cavity with a polymermatrix material to form the first material as a fiber reinforced polymermaterial comprising fiber reinforcement in a polymer matrix and thesecond material as a carbon fiber reinforced polymer material comprisingcarbon fiber reinforcement in a polymer matrix.

Exemplary methods according to the present disclosure may take advantageof a shared RTM process, as described above, or any other suitablecomposites manufacturing process that enables fiber preforms to beimpregnated by a polymer matrix material to make fiber reinforcedpolymer materials. Examples may include vacuum bagging or other resininfusion processes.

After the mold has been filled with the polymer matrix material, usuallyin liquid form, the polymer matrix material is left to solidify. Thepolymer matrix material may be thermoplastic or thermoset. In someexamples, the polymer matrix material is a thermoset resin and the moldmay optionally be heated to cure the resin.

In at least some examples of the disclosed method, the first materialhas an electrical resistivity determined by an electrically conductivefiber reinforcement and/or an electrically conductive additive in thepolymer matrix, and the second material has an elastic modulus providedby the carbon fiber reinforcement, wherein the elastic modulus of thesecond material is greater than the elastic modulus of the firstmaterial in the longitudinal direction.

Features of any example described herein may, wherever appropriate, beapplied to any other example described herein. Where reference is madeto different examples or sets of examples, it should be understood thatthese are not necessarily distinct but may overlap.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more non-limiting examples will now be described, by way ofexample only, and with reference to the accompanying figures, in which:

FIG. 1 is a schematic cross-sectional view of a composite pipe accordingto a first example;

FIG. 2 is a schematic cross-sectional view of a composite pipe accordingto a second example;

FIG. 3 is a schematic cross-sectional view of a composite pipe accordingto a third example;

FIG. 4 is a schematic cross-sectional view of a composite pipe accordingto a fourth example;

FIG. 5 is a schematic cross-sectional view of a composite pipe accordingto a fifth example; and

FIG. 6 is a schematic cross-sectional view of a composite pipe accordingto a sixth example;

FIG. 7 is a schematic cross-sectional view of a mold used in anexemplary method of making a composite pipe;

FIG. 8 a is a schematic cross-sectional view of a composite pipe withend connectors as known in the prior art; and

FIG. 8 b is a schematic cross-sectional view of a composite pipe withend connectors according to one or more examples of the presentdisclosure.

DETAILED DESCRIPTION

In the first to sixth examples disclosed herein, there is seen acomposite pipe that is hollow and may carry a pressurised fluid, forexample in use as a fuel pipe. As is seen in FIGS. 8 a and 8 b , acomposite fuel pipe is typically connected into the fuel system byfloating seals at its first and second ends. This means that any axialdisplacement, resulting from bends in the pipe undergoing deformation asa result of the pressurised flow, can result in the pipe coming loose.It is therefore desirable to stiffen the non-linear portions of the pipeto prevent deformations.

In the first example seen in FIG. 1 , a composite pipe 1 has a first end1 a and a second end 1 b with a central axis (dashed line) runningbetween the two ends 1 a, 1 b in a longitudinal direction. The pipe 1 ismade of a first material 2 extending continuously from the first end 1 ato the second end 1 b. As disclosed herein, the first material 2 is afiber reinforced polymer material having a predetermined electricalresistivity. The pipe 1 also includes a second material 4 arranged atthe two non-linear portions 6. In this example, the second material 4 islocalised at the two non-linear portions 6 and does not extend from thefirst end 1 a to the second end 1 b. As disclosed herein, the secondmaterial 4 is a carbon fiber reinforced polymer material having agreater elastic modulus than the first material 2 in the longitudinaldirection. The second material 4 therefore provides additional axialstiffness/strength at the bends in the pipe 1.

In the second example seen in FIG. 2 , the composite pipe 11 is againmade of the first material 2 extending continuously from the first end 1a to the second end 1 b. The second material 14 is arranged at the twonon-linear portions 6 and extends between the two non-linear portions 6,but does not extend continuously from the first end 1 a to the secondend 1 b.

In the third example seen in FIG. 3 , the composite pipe 21 is againmade of the first material 2 extending continuously from the first end 1a to the second end 1 b. The second material 24 is arranged at the twonon-linear portions 6 and extends from each non-linear portion 6 to thenearest end 1 a, 1 b, but does not extend continuously from the firstend 1 a to the second end 1 b.

In the examples of FIGS. 1-3 , the second material 4 is formed as alayer on the outside of the first material 2. The first material 2 formsan inner pipe.

In the following examples of FIGS. 4-6 , the second material is formedas a layer on the inside of the first material. The first material formsan outer pipe.

In the fourth example seen in FIG. 4 , a composite pipe 100 has a firstend 100 a and a second end 100 b with a central axis (dashed line)running between the two ends 100 a, 100 b in a longitudinal direction.The pipe 100 is made of a first material 102 extending continuously fromthe first end 100 a to the second end 100 b. As disclosed herein, thefirst material 102 is a fiber reinforced polymer material having apredetermined electrical resistivity. The pipe 100 also includes asecond material 104 arranged at the two non-linear portions 106. In thisexample, the second material 104 is localised at the two non-linearportions 106 and does not extend continuously from the first end 100 ato the second end 100 b. As disclosed herein, the second material 104 isa carbon fiber reinforced polymer material having a greater elasticmodulus than the first material 102 in the longitudinal direction. Thesecond material 104 therefore provides additional stiffness/strength atthe bends in the pipe 100.

In the fifth example seen in FIG. 5 , the composite pipe 111 is againmade of the first material 102 extending continuously from the first end100 a to the second end 100 b. The second material 114 is arranged atthe two non-linear portions 106 and extends between the two non-linearportions 106, but does not extend continuously from the first end 100 ato the second end 100 b.

In the sixth example seen in FIG. 6 , the composite pipe 121 is againmade of the first material 102 extending continuously from the first end100 a to the second end 100 b. The second material 124 is arranged atthe two non-linear portions 106 and extends from each non-linear portion106 to the nearest end 100 a, 100 b, but does not extend continuouslyfrom the first end 100 a to the second end 100 b.

In the examples seen in FIGS. 1-6 , the linear portions of the pipes,i.e. those portions that are not the non-linear portions 6, 106, arereferred to as “tailored conductivity regions” because only the firstmaterial is present. As is disclosed herein, the first material 2, 102has an electrical resistivity determined by an electrically conductivefiber reinforcement and/or an electrically conductive additive in thepolymer matrix, and this electrical resistivity can be tailored so as toachieve a desired overall resistance per unit length for the compositepipe.

In the examples illustrated herein, the pipes 1, 11, 21, 100, 111, 121are not linear and instead have a more complex shape, shown as includingtwo bends or non-linear portions 6, 106. However, it will be appreciatedthat the present disclosure can be applied to complex pipe shapesincludes any number of bends.

FIG. 7 schematically illustrates an exemplary manufacturing process fora pipe 1 such as that seen in FIG. 1 . In a Resin Transfer Molding (RTM)process, a two-part mold 200 a, 200 b includes a core 202 and a moldingcavity 204. In this example, one or more fiber preforms 206 for thefirst material are placed over the core 202 in the cavity 204 so as tocreate a material layer extending continuously from one end of the core202 to the other end. One or more carbon fiber preforms 208 for thesecond material are placed in the cavity 204 at the non-linear portionsi.e. bends. The two parts 200 a, 200 b of the mold are then clamped shutand a vacuum is applied while a resin such as epoxy resin is injectedunder pressure into the cavity 204. The combination of injection underpressure and the applied vacuum should draw the resin through the fiberpreforms 206, 208. Heat is then applied to the mold 200 to cure theresin. This causes the fiber reinforcement and the resin to set in theform of a solid fiber-reinforced composite pipe. The mold 200 may thenbe unclamped and opened so that the pipe including the second materialat the non-linear portion(s) can be removed. In this example, a singleshared RTM process is used to form the pipe 1.

There is seen in FIG. 8 a a schematic cross-sectional view of a straightcomposite pipe 300 with end connectors 30 as known in the prior art. Theconnectors each comprise a cylindrical hub 32, extending parallel to thecentral axis C of the pipe 300, and a flange 34, which extends in adirection perpendicular to the central axis C. The flange 34 may be usedto secure the connector 30 to another structure, e.g. an aircraft wing.

Where the hub 32 encircles the pipe 300, an elastomeric O-ring 36 islocated between the hub 32 and the pipe 300, retained between an innerwall of the hub 32 and an outer wall of the pipe 300. The O-ring 36 isconfined between a pair of retaining ridges 38 which extend radiallyoutwards from the pipe 300 at its ends. The 36 provides a seal betweenthe connector 30 and the pipe 300, such that fluid may flow along thepipe 300 and into the connector 30 without escaping. In addition, theconfiguration of the O-ring 36 allows the pipe 300 to move a smalldistance in the longitudinal direction of the central axis C relative tothe connectors 30 without compromising the seal. This enables astructure to which the connector 30 is secured to move or flex a smallamount without imparting large stresses on the pipe 300 (as would be thecase if the connector 30 were rigidly attached to the pipe 300).Instead, the pipe 300 “floats” on the O-ring 36 such that it can slidelongitudinally a small distance without breaking the seal. For example,the structure to which the connector 30 is attached may be an aircraftwing spar, which is designed to move a small amount during flight as thewing flexes due to aerodynamic load and/or temperature fluctuations. Thepipe 300 may comprise a fuel pipe located within the wing which musttherefore be able to cope with wing flex during flight.

There is seen in FIG. 8 b a schematic cross-sectional view of acomplex-shaped composite pipe 300′ with the same standard end connectors30. The more complex geometry of the pipe 300′ introduces extra demandsas there may be a tendency for the pipe 300′ to deform at its non-linearportions (i.e. bends) 306. Deflections in the composite pipe 300′ cancause the ends of the pipe 300′ to move larger distances in thelongitudinal direction of the central axis C relative to the connectors30, causing the pipe 300′ to come loose from its end connectors 30.However, this problem is addressed by using a composite pipe that hasits non-linear portions strengthened by a second material according toany of the examples disclosed herein.

Although the present disclosure has been described with reference tovarious examples, it will be understood by those skilled in the art thatvarious changes in form and detail may be made without departing fromthe scope of the disclosure as set forth in the accompanying claims.

What is claimed is:
 1. A method of making a fiber reinforced polymercomposite pipe comprising: providing a mold cavity shaped to form a pipehaving a first end, a second end, and at least one non-linear portionbetween the first end and the second end; placing one or more fiberpreforms in the mold cavity to form the fiber reinforcement of a firstmaterial extending continuously from the first end to the second end;placing one or more carbon fiber preforms in the mold at the at leastone non-linear portion to form the fiber reinforcement of a secondmaterial extending discontinuously between the first end and the secondend; and filling the mold cavity with a polymer matrix material to formthe first material as a fiber reinforced polymer material comprisingfiber reinforcement in a polymer matrix and the second material as acarbon fiber reinforced polymer material comprising carbon fiberreinforcement in a polymer matrix.
 2. The method of claim 1, wherein thefirst material has an electrical resistivity determined by anelectrically conductive fiber reinforcement or an electricallyconductive additive in the polymer matrix.
 3. The method of claim 1,wherein an elastic modulus of the second material is greater than anelastic modulus of the first material in the longitudinal direction. 4.The method of claim 1, wherein the first material is formed by automatedfiber placement (AFP).
 5. The method of claim 1, wherein the firstmaterial is formed by filament winding of the fiber reinforcement. 6.The method of claim 1, wherein the first material is formed by resintransfer moulding (RTM), using a braided preform for the fiberreinforcement.
 7. The method of claim, further comprising: forming thesecond material by filament winding of the carbon fiber reinforcement.8. The method of claim 1, comprising forming the second material byautomated fiber placement (AFP).
 9. The method of claim 1, comprisingforming the second material by braiding continuous carbon fiberreinforcement so as to achieve one or more desired fiber angles.
 10. Themethod of claim 9, further comprising: interweaving groups of continuouscarbon fibers into a triaxially braided tube comprising a first group ofcontinuous carbon fibers extending substantially along the central axisof the pipe, a second group of continuous carbon fibers extending at anangle of +50-85 degrees relative to the central axis of the pipe, and athird group of continuous carbon fibers extending at an angle of −50-85degrees relative to the central axis of the pipe.
 11. The method ofclaim 1, comprising forming the second material at the same time as thefirst material.
 12. The method of claim 11, comprising forming both thefirst material and the second material in a single RTM process.
 13. Themethod of claim 1, wherein the first material takes the form of an innerpipe or an outer pipe.
 14. The method of claim 1, wherein the secondmaterial is formed as a layer on the inside or the outside of the firstmaterial.
 15. The method of claim 1, wherein the mould cavity is shapedto form a pipe with a plurality of non-linear portions between the firstend and the second end, and the method comprises placing carbon fiberpreforms in the mould at each of the non-linear portions.